A teenage "hacktivist" has been spared jail for his part in a plot to carry out cyber attacks with the notorious Anonymous group.

Jake Birchall, 18, from Chester, was handed an 18-month youth rehabilitation order at Southwark Crown Court in London after he previously admitted conspiring to impair the operation of computers between August 1 2010, and January 22 2011.

Judge Peter Testar also sentenced the teenager to 60 hours of unpaid work and 18 months' supervision, an official confirmed.

Last week Birchall's three co-accused were all given prison sentences - one suspended - for their part in the attacks, which cost one website £3.5 million.

Christopher Weatherhead, known by the online nickname Nerdo, 22, of Holly Road, Northampton, was given the longest sentence - jailed for 18 months after being found guilty of the same charge.

Ashley Rhodes, 28, of Bolton Crescent, Camberwell, south London, was given seven months, and Peter Gibson, 24, from Castletown Road, Hartlepool, deemed to have played a lesser role in the conspiracy, was given a six-month suspended sentence.

The hacking hit financial sites including PayPal, MasterCard and Visa, which were chosen by Anonymous as part of so-called Operation Payback because the hackers did not agree with their views.

The distributed denial of service, or DDoS, attacks paralysed computer systems by flooding them with online requests. Victims' websites would be directed to a page displaying the message: "You've tried to bite the Anonymous hand. You angered the hive and now you are being stung."

The attacks cost PayPal £3.5 million in loss of trading, paying for extra staff to deal with the aftermath of the attack, and new software and hardware to defend against future attacks.

Anonymous initially targeted companies involved in anti-piracy and digital rights, including the British Recorded Music Industry (BPI), the International Federation of the Phonographic Industry (IFPI) and four sites operated by the Ministry of Sound. They then shifted their attention to PayPal, MasterCard and Visa, which would not process donations to the Wau Holland Foundation, which is involved in raising funds for WikiLeaks.